With the sudden appearance of a World Interoperability for Microwave Access (WiMax) technology, the third generation mobile communication system must improve its own network performance and reduce the cost of network construction and operation, in order to keep the competitiveness of itself in the field of mobile communication. Therefore, the standardization work group of the 3rd Generation Partnership Project (3GPP) is committed to studying the evolution of a Packet Switch Core (PS Core) and a Universal Mobile Telecommunication System Radio Access Network (UTRAN) at present. This research subject is called a System Architecture Evolution (SAE), with the purpose of enabling an Evolved Packet Core (EPC) to provide a higher transmission is rate and a shorter transmission delay, optimize grouping and support the mobility management among an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Universal Terrestrial Radio Access Network (UTRAN), a Wireless Local Area Network (WLAN) and other non-3GPP access network.
At present, the architecture of the SAE is as shown in FIG. 1, wherein a network element contained in the Evolved Radio Access Network (E-RAN) is an Evolved NodeB (eNodeB) which is used for providing radio resource to the access of a user; a Packet Data Network (PDN) is a network for providing service for a user; the EPC provides a lower delay and allows more radio access systems to access, including the following network elements:
Mobility Management Entity (MME): a control plane function entity, which is a server for temporarily storing user data, taking charge of managing and storing the context of a User Equipment (UE) (for example, UE/user identification, mobility management state, user safety parameter and on the like), allocating a temporary identification to a user, and authenticating the user when the UE is stationed in the tracking area or the network; processing all non-access stratum messages between the MME and the UE; and triggering a paging in the SAE. The MME is a mobility management unit of an SAE system; in a Universal Mobile Telecommunications System (UMTS), the mobility management unit is a Serving General Packet Radio Service (GPRS) Support Node (SGSN);
Serving Gateway (S-GW), which is a user plane entity, takes charge of user plane data routing processing, terminates downlink data of a UE in an idle (ECM_IDLE) state, manages and stores an SAE bearer context of a UE, such as an IP bearer service parameter and internal network routing information; the S-GW is an anchor point of the user plane inside the 3GPP system and a user can only have one S-GW at each moment;
PDN Gateway (P-GW), which is a gateway for taking charge of a UE accessing to a PDN, allocates a user IP address and also is a mobility anchor point of the 3GPP and non-3GPP access systems, wherein the function of the P-GW further includes policy enforcement and charging support; a user can access to a plurality of P-GWs at the same moment; and a Policy and Charging Enforcement Function (PCEF) entity also is is located in the P-GW;
Policy and Charging Rules Function (PCRF) entity, which takes charge of providing policy control and charging rules for the PCEF; and
Home Subscriber Server (HSS), which permanently stores user subscription data, wherein the content stored in the HSS includes an International Mobile Subscriber Identification (IMSI) of a UE and an IP address of the P-GW.
Physically, the S-GW and the P-GW may be combined, and user plane network elements of an EPC system include the S-GW and the P-GW.
When the coverage area in which the UE is located is changed, for example, the UE moves from a Radio Access Technology (RAT) coverage area to another RAT coverage area, the UE finds that the UE enters an unregistered area by monitoring a broadcast channel; in order to guarantee the service continuity between the UE and the core network, the UE needs to register in the new RAT coverage area; therefore, the UE would initiate a Tracking Area Update (TAU) or Routing Area Update (RAU) procedure accessing to the RAT. FIG. 2 shows a TAU procedure caused when a UE registering in a UTRAN coverage area moves into an E-UTRAN coverage area. The RAU procedure caused when a UE registering in an E-UTRAN coverage area moves into a UTRAN coverage is similar to FIG. 2. As shown in FIG. 2, the flow mainly includes the following steps.
Step 201: a UE moves into an E-UTRAN coverage area of an MME, sends a TAU request to the MME and requests to register in a new area, wherein a Packet-Temporary Mobile Subscriber Identity (P-TMSI) allocated to the UE by an SGSN is carried in the request message;
Step 202: the new MME finds an old SGSN according to the P-TMSI, and sends a context request signaling to the old SGSN to perform a context acquisition process;
Step 203: the old SGSN sends mobile management and bearer information of the user to the new MME, i.e., performs a context response;
Step 204: the new MME confirms the context after receiving the context response;
Step 205: the new MME initiates an update bearer request to an S-GW, wherein a source CPRS Tunneling Protocol-Control plane (GTP-C) tunnel identifier, a target GTP-C tunnel identifier and a binding relationship of S-GW update bearer are carried in the request message;
Step 206: the S-GW sends an update bearer request to the P-GW to transmit is address information and tunnel identifier information of the S-GW, access technology type and other parameter to the P-GW;
Step 207: the P-GW updates its own context and returns an update bearer response message to the S-GW, wherein the content of the response message includes the address, the tunnel identifier of the P-GW and the like;
Step 208: the S-GW returns an update bearer response to the new MME to bring to the MME the target GTP-C tunnel identifier designated by the S-GW, the address of the S-GW itself, and the address and tunnel information of the P-GW and the like;
Step 209: the new MME notifies an HSS of the change of a registration location through a location update message;
Step 210: the HSS keeps a single registration principle for the UE, sends a location cancel signaling to the old SGSN, and only maintains the registration of the new MME;
Step 211: the old SGSN returns a location cancel response to the HSS;
Step 212: the HSS confirms location update of the new MEE;
Step 213: if the new MME confirms that the UE is valid within a current tracking area, the new MME sends a TAU accept message to the UE;
Step 214: if the new MME allocates a new Globally Unique Temporary Identity (GUTI) to the UE through the TAU procedure, the UE would return a TAU complete message to the MME to confirm.
Based on a location update principle, if a UE moves frequently between a UTRAN coverage area and an E-UTRAN coverage area, or a frequent registration area selection is caused due to a signal intensity or the like in the same coverage area, a large number of TAU or RAU procedures will be caused, which may bring a heavy burden to an air interface. Therefore, in an EPS system, a function of Idle mode Signaling Reduction (ISR) is introduced to reduce an idle mode signaling between the UE and the core network. After the function is activated, the UE simultaneously having UTRAN and E-URTAN access functions can be registered into the MME and SGSN at the same time. In this way, when the UE moves frequently between coverage areas corresponding to two different access technologies, the UE will not initiate a TAU or RAU procedure accessing through the RAT, thereby reducing transmission of an unnecessary idle mode signaling.
The process of the UE activating the ISR is completed through the TAU or RAU procedure; however, some steps are different. The differences of the above two procedures are illustrated by taking the process of activating the ISR function through the TAU procedure for example, and the process of activating the ISR function through the RAU procedure is similar to the process of activating the ISR function through the TAU procedure. As shown in FIG. 3, the flow mainly includes the following steps.
Step 301: an UE moves into an E-UTRAN coverage area of an MME, and sends to the MME a TAU request message in which an P-TMSI of the UE allocated by an SGSN and information of whether the UE has a capability of supporting the ISR function are carried;
Step 302: a new MME finds an old SGSN according to the P-TMSI and sends a context request signaling to the old SGSN to perform a context acquisition process;
Step 303: the old SGSN sends mobile management and bearer information of the user to the new MME, and carries information of whether the old SGSN has a capability of supporting the ISR function in a returned context response message;
Step 304: the new MME judges whether to activate an ISR function according to the context information received from the old SGSN, if activating the ISR function, the new MME carries an ISR indication in a context confirmation message returned to the old SGSN, to notify the old SGSN of reserving the original context information of the UE;
Step 305: the new MME initiates an update bearer request to the S-GW, wherein a source GTP-C tunnel identifier, a target GTP-C tunnel identifier and a binding relationship of an S-GW update bearer are carried in the request message, and an indication of activating the ISR function for notifying the S-GW of reserving the bearer context information possessed by the UE at the old SGSN is further included in the update bearer request message;
Step 306: since the RAT is changed, the S-GW sends an update bearer request to the P-GW;
Step 307: the P-GW updates its own context and returns update bearer response information to the S-GW;
Step 308: the S-GW returns an update bearer response to the new MME, so as to bring to the MME the target GTP-C tunnel identifier designated by the S-GW, the address of the S-GW itself, and the address and tunnel information of the P-GW and the is like;
Step 309: the new MME notifies an HSS of the change of location through a location update message, and notifies the HSS of information of activation of the ISR function through a corresponding identification, then the HSS keeps double-registration information of the E-UTRAN and the UTRAN, and does not send location cancel information to the old SGSN again;                wherein, the above corresponding identification information is indicated as double-registration through the present location update type message unit at present;        
Step 310: the HSS judges whether the UE activates the ISR function, if the HSS does not keep the double-registration for the UE, the HSS sends a location cancel signaling to the SGSN; if the UE activates the ISR, the HSS keeps the registrations of two PS domains for the UE, and thus does not send a location cancel signaling to the SGSN; in the flow, it belongs to the latter case;
Step 311: if the SGSN receives the location cancel signaling, the SGSN returns a location cancel response to the SGSN; corresponding to the latter case in Step 310, the SGSN does not need to return the location cancel response;
Step 312: the HSS confirms location update of the new MME;
Step 313: if the new MME confirms that the UE is valid within a current tracking area, the new MEE sends a TAU accept message to the UE; in the TAU accept message, the MME notifies the UE that the ISR function is activated through an indication; and
Step 314: if the new MME allocates a new GUTI to the UE through the TAU process, the UE would return a TAU complete message to the MME to confirm.
When the ISR function is activated, both the SGSN and the MME connected to the user need to be registered in the HSS; therefore, when user data in the HSS are changed, the HSS needs to send updated user data to the SGSN and the MME. When the UE is in an idle state at both the MME and the SGSN, after the MME and the SGSN receive new user data, the MME and the SGSN initiate the bearer modification procedure after the user enters the connected state. However, if the UE enters a coverage area of a new MME or SGSN due to movement, the new MME or the SGSN can not determine whether to need to initiate a bearer modification procedure after obtaining user subscription data; in this way, a Quality of Service (QoS) used by a bearer in the new MME or SGSN does not match with a bearer QoS of an updated subscription data.